Apparatus and method for mass sterilization and pasteurization of food products

ABSTRACT

An apparatus and method for processing food products is provided. The product conditioning system includes an inlet assembly, a pressurizeable tunnel and an outlet assembly. The inlet and outlet assembly pressure vessels include a pair of vertically extending parallel screws for transporting food products from one end of the pressure vessel to the other. The pressurizeable tunnel includes a heating stage having microwave sources for irradiating food products so as to pasteurize or sterilize prepackaged food. The pressurizeable tunnel further includes a heat maintenance stage and product cooling stage. Both the heat maintenance stage and product cooling stage include vertically extending pressure vessels. Within each pressure vessel, two pairs of parallel rotating screws are positioned for moving food products through a liquid environment at a desired temperature for continued pasteurization or sterilization in the heat maintenance stage, and product cooling within the cooling stage.

RELATED APPLICATIONS

The present application is a continuation application of co-pending U.S.patent application Ser. No. 12/313,734 filed on Nov. 24, 2008.

BACKGROUND OF THE INVENTION

The present invention relates to methods and apparatus for pasteurizingor sterilizing items. More particularly, the invention relates toimproved cooking systems, preferably microwave cooking systems, having aplurality of linearly aligned segments for processing food products.

On the practical side, food processing techniques include a cycle ofselection and precooking of foods followed by a preservation cycle,which typically includes the use of refrigerators or freezers or retortcanning and, in more recent techniques, rapid heating vessels. In foodpreservation, food can be pasteurized and/or sterilized to reduce theoccurrence of food born diseases caused by harmful microorganisms.Pasteurization involves heating food to a temperature, typically between80° C. and 100° C., sufficient to kill certain pathogenic bacteria andmicroorganisms. In sterilization, food products are heated to a highertemperature, typically between 100° C. to 140° C., to ensure eliminationof more resistant microorganisms and spores. Under practical conditions,to carry out sterilization, it is necessary to heat the product to atemperature above 121° C. for a time of between 5 and 12 minutes.Preferably, the product is subsequently subjected to the most rapidpossible cooling to a temperature equal to or less than 35° C.Pasteurization and sterilization, collectively referred to herein simplyas “food processing”, allows perishable food products to be stored inrefrigerated or room temperature conditions for an extended period oftime.

More traditional methods for pasteurizing and sterilizing food productsinvolves use of convectional heating processes in which thermal energyis transferred to the food product in a high or medium temperatureenvironment utilizing hot air, hot water, or hot vapor within anoven-type construction. In some cases, where preservation on anindustrial scale is required, a post pasteurization or sterilizationphase is required which may not be limited to attenuation of microbial,pathogenic and enzymatic activity, but has the purpose of destroying allmicroorganisms present in the product, and also in the actualcontainer/package. This occurs, because the degree of resistance to heatof microorganisms is related to external and environmental factors, likethe initial microbial concentration of the medium, the characteristicsof the medium itself and the time and temperature parameters, as well asintrinsic factors related to heat sensitivity of germs and developmentstage of the cells, in which specific variations often occur. Forexample, under identical environmental conditions, it is observed thatfungi and yeast are more resistant than e. coli bacteria and, within thelatter, the rod forms are more resistant that the coccal forms.

In order to efficiently effect pasteurization and/or sterilization,microwave heating has been employed for pasteurization andsterilization. Advantageously, microwave heating can provide forpasteurization and/or sterilization in a much shorter time period thanby employing conventional heating processes. By decreasing the foodheating time, food generally tastes better and nutrient retention isimproved. In addition, microwave systems typically are more energyefficient than conventional heating systems.

Great Britain Patent No. 1103597 (Newton et al.) describes a microwaveheating system for controlling microorganisms in prepared foods andbeverages. It prescribes for exposure of the already prepared foods toelectromagnetic waves with a frequency of 20-40 MHz at an intensity of500-3000 volts for a sufficient period of time to attenuate themicroorganisms present in the manufactured product. The use of microwaveenergy to sterilize materials is known in even greater detail. Forexample, WO0102023 (Korchagin) proposes a generator that has thecapacity to implement the intensity of the electromagnetic field at alevel to ensure destruction of microorganisms.

Complex apparatuses, specifically continuous treatment tunnels forsanitization of packaged products, have been known since at least 1973.For example, U.S. Pat. No. 3,747,296 (Zausner) proposes an apparatuswith linear development, in which filled containers are introduced andsubsequently closed. The containers are passed through the tunnel, whichis subdivided into different treatment zones at temperatures between 90°C. and 150° C. Means of irradiation are also provided, which have thepurpose of sterilizing the cover only. Similarly, U.S. Pat. Nos.5,066,503; 5,074,200; 5,919,506 and 6,039,991 issued to Ruozi describeconveyor driven microwave processing plants for pasteurizing, cookingand sterilizing food products. The systems include a plurality ofchambers wherein the temperature and pressure are controllably elevatedand decreased as the food products travel from chamber to chamber.

U.S. Pat. No. 3,889,009 (Lipoma) describes a conditioning tunnel forfoods previously prepared in bowls and sealed under pressure. At theentry and exit of this tunnel, corresponding to the crossing point ofthe manufactured vessels, pressure closure doors are provided. Once thesealed vessels have entered the interior of the tunnel, each vesselundergoes a sterilization treatment, passing beneath a source ofelectromagnetic waves. Each vessel is then transferred downline, alwaysby means of a common belt or chain conveyor, to pass through a coolingunit. A device to generate pressure during the sterilization phaseoperates within the apparatus to avoid a situation in which theproducts, because of the process, burst because of the dilation effect,or from seal failure. This phenomenon most frequently entails escape ofliquid from individual containers, producing not insignificant drawbackswithin the apparatus, like accumulation of dirt and the subsequent needto carry out frequent maintenance.

Other microwave tunnel apparatuses are also known. For example, Italiancompanies Modo Group International from Brescia Italy and Micromac fromReggio Emilia developed automatic and computerized food processingtunnels which provided for receiving the products, in this case prepareddishes in a heat-sealed vessel, and for carrying out the fundamentalphases of sterilization treatment. The tunnels include elongatecylindrical constructions have diametrically round cross sections,within which, corresponding to the different stages, the followingprocess phases were conducted: 1) preheating; 2) sterilizing usingdevices that generate microwaves; 3) holding or stabilization of theproduct at the sterilization temperature for a specified time (microwavesources, which are positioned along the lower side of the conditioningtunnel beneath or corresponding to the plane of advance of the preparedfoods, are typically provided to execute at least these last twophases); and 4) cooling before unloading. At the end of the process, afinished product emerges, sterilized and ready to be packaged and storedin warehouses.

More recently, U.S. Pat. No. 7,119,313, assigned to Washington StateUniversity Research Foundation, describes a tunnel for pasteurizingand/or sterilizing food. The tunnel includes a plurality of chambers inwhich microwave sources are positioned on each side of a microwavecavity in which food products are heated. This reference describespressurizing the microwave cavity and filling it with a liquid in aneffort to balance the pressure generated in the food packaging totherefore prevent the packaging from bursting or otherwise opening.

Unfortunately, the aforementioned food processing systems suffer fromnumerous disadvantages. Foremost, though several of the prior artreferences describe pressurized food processing chambers, none of thereferences describe an efficient manner for introducing products into amicrowave tunnel without a significant loss of internal pressure to theexternal environment as packages are introduced. Presumably in practice,the prior art systems require that the pressurizeable chambers be openedfor the introduction of food products. Thereafter, the chambers areclosed and pressurized to a desired pressure while subsequently orsimultaneously activating a microwave heating source for heating theproducts. Presumably, the food products are expelled from the foodprocessing system in similar manner requiring that the heating chambersbe depressurized, one or more doors opened and the products transportedfrom inside the heating chamber to exterior to the heating chamber. Thenegative implications from this time consuming and complicatedintermittent process has made commercialization of pressurized microwavepasteurization and sterilization impractical.

Thus, there is plainly a need for a food processing system which willefficiently and economically provide for the introduction andtransportation of food products through a pressurized microwave cookingprocess.

Advantageously, the food conditioning system would not require the timeconsuming and impractical process of continuously pressurizing anddepressurizing various heating cavities for the introduction andexpulsion of food products and their packages.

Even more advantageously, a preferred food conditioning system wouldprovide for efficient holding and cooling chambers for maintaining andcooling products at desired temperatures while permitting the productsto continuously move, without starting and stopping, to increaseefficiency.

SUMMARY OF THE INVENTION

Briefly, in accordance with the invention, an improved apparatus andmethod for processing products is provided, primarily for foodpasteurization and sterilization. The conditioning system is especiallyadapted for the processing of food in trays or bowls which have beenpreviously sealed.

The product conditioning system is subdivided into variouspressurizeable stages including an inlet assembly stage, a tunnelsection including at least one heating stage for heating products, aswell as an outlet assembly. Preferably, the pressurizeable tunnel isalso divided to include a temperature maintenance stage for maintainingthe products at a desired temperature for a desired time period, as wellas a cooling stage for cooling the food products to a desiredtemperature. The heating stage includes one or more microwave sourcesand accompanying wave guides for heating the food products. In addition,the pressurizeable tunnel is preferably connected to an active pressurecontrol system for providing pressure equalization within the heatsealed packages. The active pressure control system may incorporatevarious structures known to those skilled in the art including, but notlimited to, the use of pressurized cylinders, electric or combustionpowered gas compressors, or hydraulic compressors, all of which maypreferably be controlled by computer processors. The microwave sourcesmay also be constructed in various configurations as can be determinedby those skilled in the art. Preferably, the heating chamber has aquadrilateral cross-section and the microwave sources provide bothtop-side irradiation and bottom-side irradiation for products conveyedthrough the quadrilateral tunnel.

The pressurizeable tunnel and corresponding heating chamber is liquidand gas tight from the outside environment so as to be pressurizeable,and preferably fillable with a liquid such as water. To maintainpressure within the heating chamber, the product conditioning unitincludes an inlet assembly providing a pressure seal as well as anoutlet assembly providing a pressure seal while the packages areconveyed throughout the sterilization system.

The inlet, heating, temperature hold, cooling and output sections may beoriented in any direction as the system does not rely on gravity in itsmethod of transport within the system. It is desirable for the Inputentry opening and output exit opening to be located at the highest pointin the system to minimize air introduction into the system. Verticalpositioning may be desirable in most factory settings to minimize floorarea footprint.

The inlet pressure assembly includes a pair of what are referred toherein as “screwstacks”. Each screwstack includes a hollow pressurevessel which is preferably cylindrical and positioned vertically. Eachscrewstack further includes an entry opening, openable and closeable bya door, for introduction of food products. In addition, each screwstackincludes a exit opening, which is openable and closeable by a seconddoor, for the expulsion of food products from the interior of eachscrewstack. The exit opening of each inlet assembly screwstack isconnected to the pressurizeable tunnel by sealed conduits orintermediate chambers.

Preferably, each screwstack is cylindrical and positioned verticallywith a first entry opening projecting through the screwstack's sidewallnear the top of the screwstack. Conversely, preferably the inletassembly's screwstacks have their exit openings positioned to projectthrough the sidewalls near each screwstack bottom.

Each of the inlet assembly screwstacks include a pair of verticallyextending threaded screws positioned within the screwstack's hollowinterior. Each screw is rotatable and positioned parallel to one anotherwith a space between them so that product packages can be receivedwithin the screwstack threads. After passing through the screwstackentry door and upon rotation of the parallel screws, packages areconveyed from the inlet assembly's entry opening to the inlet assembly'sexit opening so as to be conveyed to the conditioning unit'spressurizeable tunnel.

The outlet assembly has a similar construction to the inlet assembly.Specifically, the outlet assembly includes two hollow screwstackassemblies which include cylindrical pressure vessels which arepositioned to extend vertically. Each of the outlet assembly screwstacksalso include a first entry opening and a second exit opening, openableand closeable by corresponding gaseous tight doors. As opposed to theconstruction of the inlet assembly, preferably each of the outletassembly screwstacks' entry openings is positioned near the bottom ofthe screwstack and the exit opening is positioned at the screwstack'supper extremity. Each of the outlet assembly screwstacks also includes apair of vertically extending screws positioned parallel to each otherand spaced so as to position food packages between the threads ofadjacent screws. Again, rotation of the parallel thread causes the foodproducts to be transported downline through the outlet assembly from thescrewstack's first entry door to the screwstack's second exit door.

The inlet assembly, pressurizeable tunnel including heating stage, andoutlet assembly form a liquid and gas tight enclosure. Of importance, inorder to maintain increased pressure within the pressurizeable tunnel,the inlet assembly and outlet assembly screwstacks are constructed sothat the first entry door is closed when that screwstack's second exitdoor is opened, and similarly the screwstacks are constructed so thattheir second exit doors remain closed when their respective first entrydoors are opened.

Preferably the doors are controlled by mechanical actuators connected toa control processor. The control processor may take various formsincluding all software and processing conducted within a single computerchip. Alternatively, the control processor may utilize a plurality ofprocessors connected to actuators for opening and closing the variousscrewstack doors. Preferably, the control processor also controls therotation of the various screwstack screws so as to selectively rotateand transport packages from downline through the product's conditioningunit.

In operation, an inlet assembly first screwstack is loaded with packagesby the control processor opening a screwstack first entry door whilemaintaining that screwstack's second exit door in a closed condition.The screwstack's internal screws are rotated to receive food products,preferably encapsulated in food packaging, into the interior of thescrewstack. The parallel screws are rotated until the screwstack isfilled with food products. The screwstacks can be constructed to storeany number of prepackaged food products. However, it is preferred thateach of the screwstacks is capable of storing and stacking at least 10food products. Even more preferably, each screwstack is capable ofstoring and stacking 50 or more food products. Once the inlet assemblyfirst screwstack is filled with food products by rotation of theinternal screws, the first entry door is closed, pressure equalizationoccurs to match the system's internal pressure and thereafter thescrewstack's second exit door is opened. Of importance, at least onedoor of a screwstack is closed at all times to maintain a pressure sealwithin the entire assembly. Once the inlet assembly's second door hasbeen opened, the screwstack's internal screws are again rotated toconvey the food products downline through the system. Preferably, amechanical actuator or the like is positioned within the screwstack tomove packages from interior of the screwstack downline into thepressurizeable tunnel's heating stage. Once the screwstack has beenemptied of food products, the screwstack exit door is closed andthereafter the screwstack's entry door is opened for once againintroduction of food products into the screwstack.

In order to continuously convey food products through the productconditioning unit and heating stage without stopping for a firstscrewstack to refill with food products, the operation of the respectiveinlet assembly screwstacks is alternated so that while one screwstack isreceiving and loading products into its interior, the other screwstackis expelling products from its interior into the pressurizeable tunnel.More specifically, the controller controls the second screwstack to loadfood products into the interior of the second screwstack while the firstscrewstack is conveying products from interior to its screwstack intothe pressurizeable tunnel. Thereafter, the controller causes the secondscrewstack to convey products through its exit opening while the firstscrewstack is loading food products into its interior.

The conditioning system's outlet assembly provides for the expulsion ofthe food products from the pressurizeable tunnel in similar manner tothe inlet assembly introducing food products into the pressurizeabletunnel. Specifically, the outlet assembly's screwstacks alternativelyoperate to fill with products by opening their first entry door androtating the internal screws to receive food products into thescrewstack's interior. Simultaneously, the other screwstack has itssecond exit door opened and its internal screws are rotated to moveproduct out the second exit door. Again, when a screwstack's entry dooror exit door is opened, its corresponding exit or entry door is closedto maintain a liquid and/or gas tight environment within thepressurizeable tunnel; pressure equalization also occurs to match thesystem's internal pressure.

Preferably, the pressurizeable tunnel includes one or more stages formaintaining food products at a desired temperature for a desired timeperiod. Preferably, a temperature maintenance stage is constructed toinclude one or more vertically extending cylindrical screwstacks. Eachmaintenance stage screwstack includes an entry opening for the receiptof food products and an exit opening for the expulsion of food products.Preferably, the maintenance stage screwstack includes two pairs ofvertically extending threaded screws positioned within the screwstack'scentral cavity. Preferably, the maintenance stage screwstack's entry andexit openings are positioned near the same extremity of the screwstack.

A first pair of parallel screws are positioned to hold products betweenthe parallel screws so as to convey food products from the entry openingto the opposite extremity of the screwstack. Thereafter, a mechanicalactuator located within the screwstack forces food products from thefirst pair of screws to the second pair of screws. Products encounteringthe second set of screws are then conveyed in the opposite direction asprovided by the first set of screws until products are conveyed theentire length of the screwstack toward the screwstack's exit door wherethey are then expelled to another stage of the pressurized tunnel orexpelled to the outlet assembly for expulsion from the productconditioning unit.

The pressurized tunnel may have any number of temperature maintenancescrewstacks forming heating stages and/or cooling stages. In a preferredembodiment, the pressurizeable tunnel has one to three maintenancescrewstacks for maintaining the food product at a sufficiently hightemperature to provide food sanitization, such as at a temperature ofabove 121° C. Preferably the pressurizeable tunnel also has severaltemperature maintenance screwstacks for cooling the products to roomtemperature or below. In a preferred embodiment, the pressurizeabletunnel has four to seven temperature maintenance screwstacks positionedimmediately upline to the outlet assembly which are dedicated to coolingthe product for expulsion from the food processing system.

Preferably, the conveyor system for transporting products through thefood processing system is fully automated and controlled by the controlprocessor, for moving products downline through the system. In addition,the automated conveyer system may include various mechanical apparatus,such as a belt drive, for conveying food products through thepressurizeable tunnel including its horizontally aligned heating stage.In a preferred embodiment, a belt drive is employed in which parallelbelts engage the sides of the products without any mechanical apparatusengaging the top or bottom of the product to convey products through theheating stage. A preferred drive belt system is described in a pendingU.S. Provisional application entitled ‘Package Conveyor for ContinuousProcess Microwave Applicator’, U.S. Provisional Ser. No. 61/192,687filed Sep. 19, 2008, which is hereby incorporated by reference in itsentirety.

The present invention optimizes the sterilization cycles of foodproducts including heating, temperature stabilization and cooling whilewithin a pressurized environment to inhibit package bursting or leaking.This objective is made possible by providing a product conditioning unitallowing for the introduction of food products and expulsion of foodproducts through a pressurized environment without having to pressurizeand depressurize the system with the introduction of new products.

Advantageously, the food conditioning system of the present invention isa commercially-compatible continuous process that is inexpensive tomanufacture, economically efficient to prepare food products for sale,and fits within a small manufacturing footprint.

The invention is an efficient method of providing a continuous flow ofproduct into and out of a pressurized conditioning unit. This inventionis a significant improvement to a microwave system providing an even andconstant flow of product through the energy exposure areas, improvingenergy absorption patterns, process efficiencies and product quality.

These and other advantages of the invention will be apparent from thedetailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the food processing system of thepresent invention;

FIG. 2 is a perspective view of the food processing system's inletassembly of the present invention;

FIG. 3 is a rear close-up perspective view of the food processingsystem's inlet assembly illustrated in FIG. 2;

FIG. 4 is a rotated close-up perspective view of the food processingsystem's inlet assembly shown in FIG. 2 illustrating the conveyance offood products into the inlet assembly;

FIG. 5 is a perspective view of the food processing system's temperaturemaintenance screwstacks of the present invention;

FIG. 6 is a perspective view of the food processing system's heatingstage of the present invention;

FIG. 7 is a perspective view of the food processing system's outletassembly of the present invention;

FIG. 8 is a close-up perspective view of the food processing system'soutlet assembly illustrating the conveyance of food products;

FIG. 9 is a perspective view of a tray for holding food for use with thefood processing system of the present invention;

FIG. 10 is a perspective view of a food product including food,packaging tray and cover for use with the food processing system of thepresent invention.

FIG. 11 is a perspective view of the food processing system's of thepresent invention wherein the inlet assembly and outlet assembly havescrewstacks positioned side-by-side in an upline to downlineconfiguration;

FIG. 12 is a close-up perspective view illustrating the inlet assemblyhaving inlet screwstacks positioned side-by-side in an upline todownline configuration;

FIG. 13 is a close-up perspective view illustrating the outlet assemblyhaving outlet screwstacks positioned side-by-side in an upline todownline configuration; and

FIG. 14 is a perspective view of the drive belt system for conveyingfood products through the heating stage.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention is susceptible of embodiment in variousforms, as shown in the drawings, hereinafter will be described thepresently preferred embodiments of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe invention, and it is not intended to limit the invention to specificembodiments illustrated.

With reference to the figures, the food processing system 1 includesthree primary components comprised of an inlet assembly 6, anintermediate pressurizeable tunnel section 35, and an outlet assembly 8.The inlet assembly 6 provides for the introduction of food products intothe food processing system without requiring depressurization of thepressurizeable tunnel. Similarly, the outlet assembly provides for theexpulsion of food products from the food processing system withoutrequiring depressurization of the pressurizeable tunnel.

With reference primarily to FIGS. 1-4 and FIGS. 11-13, the inletassembly 6 includes a pair of inlet screwstacks 7 a and 7 b. Asillustrated in FIGS. 1-4, the screwstacks 7 a and 7 b may be positionedlaterally adjacent to one another relative to the longitudinal path ofthe food processing system 1. Alternatively, as illustrated in FIGS.11-12, the screwstacks 7 a and 7 b may be positioned longitudinallyadjacent to one another relative to food processing system 1.

Each of the screwstacks includes a hollow pressure vessel 13 which ispreferably vertically aligned. As illustrated best in FIG. 4, eachscrewstack further includes an entry opening 17, openable and closeableby a door 18, at its upper extremity for the introduction of foodproducts 31. Of importance, the door 18 provides a liquid and gaseoustight seal so that the screwstack can be pressurized. With reference toFIG. 2, at the bottom of each inlet screwstack 7 a and 7 b, a secondopening 19 is provided which is openable and closeable by an exit door.Again, the exit door provides a liquid and gaseous tight seal when thedoor is closed.

Each of the inlet screwstacks 7 a and 7 b further includes a pair ofvertically extending threaded screws 21 positioned within thescrewstacks' hollow interior. Each screw 21 is rotatable by a motor 15and includes a plurality of threads 23. The screws are positionedparallel to one another to provide a space sized so that products can bepositioned and maintained between the adjacent threads 23 of therespective screws 21. The rotation of the screws causes food products 31to move vertically through the inlet screwstack's interior. Morespecifically, food products 31 are introduced into each inletscrewstack's entry opening 17 when the entry door 18 is in an opencondition. Rotation of the screws 21 causes food products to betransported downline from the screwstack's entry opening 17 to thescrewstack's exit opening. As illustrated in FIG. 3, verticallyextending alignment rods or other guide assemblies 16 may be employed toproperly maintain the products 31 between the parallel screws whiletraveling vertically within the screwstack.

Of importance, the inlet assembly screwstacks are operated so that thefirst entry opening 17 is closed by the entry door 18 when therespective screwstack's second exit opening is opened. Conversely, theoperation of the screwstacks is controlled so that in the event that theentry opening 17 is open then the screwstack's second exit opening 19 isclosed by an exit door 20.

With reference to FIGS. 3 and 4, in order to continuously introduce foodproducts into the food processing system 1, the operation of the inletassembly's respective screwstacks 7 a and 7 b is alternated so thatwhile one screwstack is receiving and loading food products 31 into itsinterior, the other screwstack is expelling products through aconnecting conduit 37 into the pressurizeable tunnel 35. To introducefood products into the inlet assembly screwstacks 7 a and 7 b, the foodprocessing system preferably includes a conveyor 27 connected to aninlet hopper 23. The inlet hopper 23 and conveyor 27 transport foodproducts to a sorting chamber 29 which utilizes an internal mechanicalactuator (not shown) to selectively introduce food products into ascrewstack 7 a or 7 b.

As illustrated in FIGS. 1, 2, 11 and 12, preferably the inlet assembly 6also includes a second sorting chamber 29 connected to the inletscrewstack's exit openings 19 for receiving food products 31 from thescrewstacks 7 a and 7 b for transportation to the pressurizeable tunnel35. Again, the exit openings 19 of the inlet screwstacks 7 a and 7 b arealternately opened for expulsion of food products 31 into the sortingchamber 29, which in turn includes an internal mechanical actuator (nowshown) that transports the food products through a liquid and gaseoustight connecting conduit into the pressurizeable tunnel 35.

The pressurizeable tunnel 35 can take various forms. For example, asillustrated in FIGS. 1 and 5, the pressurizeable tunnel may besubdivided into numerous chambers for product processing. Anyconstruction of a pressurizeable tunnel will include at least oneheating stage 41. As illustrated in the figures, the heating stage 41includes at least one microwave source 43, preferably including aplurality of microwave generators 45 and wave guides 47. As illustratedin the figures, a preferred microwave source 43 includes four microwavegenerators 45 and corresponding wave guides 47 for directing microwaveenergy downwardly upon the top of food products, and an additional fourmicrowave generators 45 and corresponding wave guides 47 for directingmicrowaves upwardly upon the bottom of food products. The food productsmay be conveyed through the heating stage 41 using a wide variety ofmechanical apparatus as can be selected by those skilled in the art. Asillustrated in FIGS. 6 and 14, in a preferred embodiment, food products31 are conveyed through the heating stage without any mechanicalapparatus engaging the top or bottom of the products by utilizing a pairof parallel belts having elongate slots sized and positioned to receivethe edges of product trays effectively eliminating all massivemechanical conveying apparatus from the microwave exposure area 34.

With reference to FIG. 14, the system for conveying food productsthrough the heating stage preferably employs a conveyor belt systemwhich is mostly disposed within the pressurizeable tunnel's heatingstage 41. More particularly, the conveyor system 6 consists primarily ofa pair of parallel side-by-side belts 60-L and 60-R which are spacedapart to engage the sides of packages. Preferably, the packages aresupported only by the belts 60 and by any buoyancy imparted by the fluidwith the heating stage. Preferably, all other mechanical supports orother apparatus are eliminated or spaced a significant distance awayfrom the packages to reduce interference to the microwave field. Thus,the conveyor belts 60 support packages 31 so that the packages 31 arespaced above any apparatus such as the bottom wall of the pressurizeabletunnel 35 while the packages are conveyed through the microwave field.

As illustrated in FIG. 14, a motor 70 and series of belts, gears, andpulleys are used to drive the pair of conveyor belts 60 in synchronism.In particular, these may include a timing belt 74 and first timing beltpulley 79 coupled to motor 70 via drive gears 78 and drive shaft 80. Asecond timing belt pulley 79 on the far side operates belt drive roller73. Belt drive roller 73 and various belt guide rollers 72 furtherprovide movement and support for the conveyor belts 60. As illustrated,the motor 70 may be supported by motor bracket 75 above gears 78, pulley79 and drive shaft 80, but it should be understood that otherarrangements are possible.

In operation, a left hand belt 60-L is continuously fed around itsrespective guide rollers 72 and drive roller 73 (driven by timing belt74), and a respected right hand belt 60-R is continuously fed around itsrespective drive roller 73 (driven by one of the gears 78) and itsrespective guide rollers 72. Left hand belt 60-L and right hand belt60-R are thus kept in alignment with one another via gears 78, pulleys79 and timing belt 74. This is necessary to ensure that the packages 31are conveyed in an orderly fashion.

Though not illustrated, a tension measurement device or other devicesuch as a motion transducer may be used in combination with the belts 60to provide feedback on package location and condition. The tensionmeasurement devices can be located as part of one of the guidancerollers 72, within the heating stage, or may be part of one of the drivepulleys 72 which may be located outside the heating stage. In addition,belt tensioners may be used to prevent slack in the belts 60.Furthermore, the belts 60 may be perforated to receive sprockets or tabsformed upon drive roller 73 and/or guide roller(s) 72. The sprocketswill engage the perforated holes to provide a more positive engagementmechanism between motor 70 and belts 60. The belts themselves arepreferably made of a suitable material that is temperature, fluid andmicrowave energy insensitive. Teflon™, Kevlar™ and fiberglass areexamples of suitable materials.

As illustrated in FIGS. 6, 9 and 10, preferably the food products 31include a bottom tray 34 and a peelable cover 33 for encapsulating afood product 32. Each of the trays include parallel side lips 36 whichextend beyond the traditional edge of the tray for being received withinthe belt slots.

The pressurizeable tunnel 35 may include a heat maintenance stage 49 formaintaining food products at a desired temperature for a desired timeperiod to kill pathogenic bacteria, spores, and organisms. Thepressurizeable tunnel may also include a product cooling stage 51 forcooling products from high temperatures to lower temperatures forultimate expulsion from the food processing system 1. The temperaturemaintenance stage, including the sub-stages for heating and cooling ofproducts, utilize temperature maintenance screwstacks 11.

As illustrated in FIGS. 5 and 7, each of the temperature maintenancescrewstacks 11 preferably include two pairs of screws 21, as opposed toa single pair of screws within the inlet and outlet assemblyscrewstacks. Within the temperature maintenance screwstacks 11, a firstpair of screws 21 receives the food products 31 which have beenintroduced into the screwstack through an entry opening 37. The screws21 are rotated by one or more motors 15 to transport the food products31 upwardly to the opposite upper extremity of the screwstack where thefood products are moved laterally by a mechanical actuator (not shown)to the upper extremity of the other pair of screws 21. The second pairof screws 21 transport the food products downwardly to the bottom of thescrewstack 11 until they are ejected by an additional mechanicalactuator to an exit opening 19 where they are expelled to an additionaltemperature maintenance screwstack 11 or introduced into the outletassembly 8. (See FIG. 7).

Advantageously, the temperature of maintenance screwstacks 11 provide avery small footprint, but a significant travel distance for the foodproducts so that food products are maintained at a proper temperaturefor a desired time period. As illustrated in FIG. 1, in a preferredembodiment, the heat maintenance stage 49 includes 3 screwstacks 11 forproviding a passageway within which the food products will travel for asufficiently long time period at a desired temperature sufficient tokill pathogenic microorganisms and spores. Meanwhile, a preferredproduct cooling stage 51 includes 4 screwstacks 11 providing sufficienttravel time and distance for the products to cool to a desiredtemperature before being introduced into the food processing system'soutlet assembly 8.

As illustrated in FIGS. 7 and 8, the outlet assembly 8 receives the foodproducts 31 from the product cooling stage 51 through a connectingconduit 37. With reference also to FIGS. 11 and 13, the outlet assembly8 has a construction very similar to the construction of the inletassembly 6. Specifically, the outlet assembly includes a pair ofscrewstacks 9 a and 9 b. Like, the inlet assembly 6, the outletscrewstacks 9 a and 9 b may be positioned laterally adjacent to oneanother relative to the longitudinal path of the food processing system1 as illustrated in FIGS. 1 and 7. Alternatively, as illustrated inFIGS. 11 and 13, the outlet screwstacks 9 a and 9 b may be positionedlongitudinally adjacent to one another relative to food processingsystem 1. In addition, the outlet assembly includes a sorting chamber 29which receives the food products from the product cooling stage 51 andconveys the food products to either the first or second outletscrewstack 9 a or 9 b. Each outlet screwstack includes a pair of screws21 for transporting the food products from the screwstack's bottomextremity to the screwstack's top extremity. Each of the screws isrotated by motors 15 illustrated at the top of the screwstack. Afterbeing transported to an outlet screwstack's upper extremity, amechanical actuator or the like forces the food products through an exitopening 19 formed in the screwstack sidewall to a sorting chamber 29.The sorting chamber 29 receives the food products 31 from either thefirst or second screwstack 9 a or 9 b, which in turn conveys the foodproducts to an exit hopper 25. A conveyor belt 27 then transports thefood products 31 from the exit hopper 25 for distribution.

The outlet assembly's screwstacks' inlet openings 17 near the bottom ofthe screwstacks and exit openings 19 near the top of the screwstacks areopenable and closeable by an entry door 18 and exit door 20,respectively. Each of these doors provide a substantially liquid andgaseous tight seal so that the outlet screwstacks 9 a and 9 b can befilled with a liquid and pressurized. In the event that an outletscrewstack entry opening is open, the respective screwstack's exitopening is closed by the exit door 20. Conversely, in the event that theexit opening 19 is in an open condition, the outlet assembly's entryopening 17 is closed by an entry door 18. Thus, at least one of theoutlet screwstack's doors are closed at any one time so as to maintainpressure within the pressurizeable tunnel 35.

In operation, the outlet assembly also operates in similar manner to theoperation of the inlet assembly. The outlet screwstacks 9 a and 9 b areoperated alternately so that as a first outlet screwstack 9 a receivesfood products 31 through a sorting chamber 29 from the product coolingstage 51, the other screwstack 9 b expels food products from its hollowinterior to a second sorting chamber 29 for transportation to the exithopper 25.

In order to control the various conveying apparatus, lever arms,mechanical actuators, and entry and exit doors, the food processingsystem 1 includes a control processor. The control processor can bedesigned by those skilled in the art without undue experimentation. Thecontrol processor may include one or more computer chips and one or moresoftware programs for controlling the rotation of the screwstack screws,movement of the conveyor belts, movement of the mechanical lever armsand actuators, and opening and closing of the entry and exit doors so asto continuously move food products 31 through the food processing system1.

In operation, preferably the entire food processing system, includinginlet assembly 6, pressurizeable tunnel 35, and outlet assembly 8, isfilled with a liquid such as water. As illustrated in FIG. 7, the waterline 53 within the inlet and exit hoppers is sufficiently high so as tobe above the chamber's entry or exit openings so that unwanted aircannot be introduced into the system. In addition, the food processingsystem includes an active and controllable pressure source (not shown)for maintaining the pressurizeable tunnel at an increased pressure,preferably at or above two atmospheres. The active pressure controlsystem may include the use of pressurized cylinders, electric orcombustion powered gas compressors, or hydraulic compressors, all ofwhich may be controlled by the control processor.

While several particular forms of the invention have been illustratedand described, it will be apparent that various modifications can bemade without departing from the spirit and scope of the invention. Forexample, the inlet, outlet and temperature maintenance screwstacks maybe of any length and may store any number of food products. Preferably,the screwstacks are sufficiently tall to hold at least 10 food productswithin its interior. Even more preferably, each screwstack issufficiently tall so as to hold 50 products or more within its interior.In the preferred embodiment, the screwstacks are sufficiently long thateach pair of screws 21 which are approximately 8 feet long for storingapproximately 60 packaged food products within the screw threads. Thus,preferred inlet and outlet screwstacks can store approximately 60 foodproducts within their interior, while each maintenance screwstacks, withtheir two pairs of screws, can store approximately 120 food productswithin its interior.

Various changes to the conveyor system may also be made withoutdeparting from the spirit and scope of the invention. For example, thepreferred embodiments described herein include a single conveyor beltsupplying or retrieving food products to or from a hopper and sortingchamber. However, the sorting chamber may be eliminated by providing theinlet and/or outlet screwstacks with individual belts or the like tosupply or receive food products.

Since changes can be made without departing from the spirit and scope ofthe invention, it is not intended that the invention be limited exceptto the following claims. Having described my invention in such terms soas to enable persons skilled in the art to understand the invention,recreate the invention and practice it, and having presently identifiedthe preferred embodiments thereof,

I claim:
 1. A screwstack prepackaged product transportation systemcomprising: a first hollow vessel having first and second ends, andhaving an inlet at said first end for introduction of prepackagedproducts and an outlet at said first end for the expulsion ofprepackaged products; and a first pair of parallel screws positionedwithin said first hollow vessel for receiving prepackaged products atsaid first end and for engaging and transporting prepackaged productsfrom said first end to said second end; and a second pair of parallelscrews positioned within said first hollow vessel for receivingprepackaged products at said second end from said first pair of parallelscrews and for engaging and transporting prepackaged products from saidsecond end back to said first end for expulsion from said outlet.
 2. Thescrewstack prepackaged product transportation system of claim 1 whereinsaid first hollow vessel is elongate and positioned vertically.
 3. Thescrewstack prepackaged product transportation system of claim 1 whereinsaid first hollow vessel is elongate and positioned vertically, and saidinlet and said outlet are positioned at the bottom of said vessel. 4.The screwstack prepackaged product transportation system of claim 1wherein said first hollow vessel is filled with a liquid.
 5. Thescrewstack prepackaged product transportation system of claim 1 whereinsaid first hollow vessel holds a plurality of prepackaged products. 6.The screwstack prepackaged product transportation system of claim 1wherein said first hollow vessel holds at least 10 prepackaged products.7. A method of transporting prepackaged products comprising the stepsof: providing a screwstack comprising a first hollow vessel having firstand second ends and having an inlet at the first end for introduction ofprepackaged products, and an outlet at the first end for the expulsionof prepackaged products, the screwstack further comprising a first pairof parallel screws positioned within the first hollow vessel forreceiving prepackaged products at the first end and for engaging andtransporting prepackaged products from the first end to the second end,and the screwstack further comprising a second pair of parallel screwspositioned within the first hollow vessel for receiving prepackagedproducts at the second end from the first pair of parallel screws andfor engaging and transporting prepackaged products from the second endback to the first end for expulsion from the outlet; providing productspackaged within packaging to form prepackaged products; positioning theprepackaged products in the inlet so as to simultaneously engage each ofthe first pair of parallel screws; transporting the prepackaged productsfrom the inlet to the second end of the vessel by rotating each of thefirst pair of parallel screws; and transporting the prepackaged productsfrom the second end of the vessel to the outlet for expulsion byrotating each of the second pair of parallel screws.
 8. The method oftransporting prepackaged products of claim 7 wherein said first hollowvessel is elongate and positioned vertically.
 9. The method oftransporting prepackaged products of claim 7 wherein said first hollowvessel is elongate and positioned vertically, and said inlet and saidoutlet are positioned at the bottom of said vessel.
 10. The method oftransporting prepackaged products of claim 7 wherein said first hollowvessel is filled with a liquid.
 11. The method of transportingprepackaged products of claim 7 wherein said first hollow vessel holds aplurality of prepackaged products.
 12. The method of transportingprepackaged products of claim 7 wherein said first hollow vessel holdsat least 10 prepackaged products.